1. Field of the Invention
The present invention relates to an articulated arm.
2. Explanation of Related Art
This kind of articulated arm for manipulator is shown, for example, in FIG. 10 (see, for example, Japanese Patent Publication H7-80145). The articulated arm shown in FIG. 10 comprises an elastic shrinking element (actuator) 23 of three members single-unit supported between a first arm member 21 and a second arm member 22 coupled by a ball joint 20. The ball joint 20 is composed of a socket 20a having a hemispherical recess, and a ball 20b freely rolling and fitting in this recess. The elastic shrinking element 23 is expanded in diameter and deformed when a pressurizing fluid is supplied from a pressure supply source not shown, so as to shrink in the longitudinal direction. Each elastic shrinking element 23 is coupled to the first arm member 21 at one end, and to the second arm member 22 at other end. For their coupling, one end of each elastic shrinking element 23 is coupled to a mounting member 24 affixed to the first arm member 21 by a wire 25a, and other end is coupled to the second arm member 22 by a wire 25b. Pressurizing fluid is supplied or discharged in the elastic shrinking element 23 to apply tension to each wire 25b, and the second arm member 22 is moved to the first arm member 21 by way of the ball joint 20. When the second arm member 22 is moved to a specified position, a negative pressure is applied to the gap between the inner side of the socket 20a and the ball 20b by a pressurizing fluid supply and discharge device 26, and the second arm member 22 is stopped and held at this position.
Therefore, in the conventional articulated arm, holding of the second arm member 22 at specified stopping position is achieved by the balance of tension of all of the plurality of wires 25b, but when the second arm member 22 unexpectedly hits against an object (obstacle), the elastic shrinking element 23 or the object may be damaged or broken by this impact.
Also, to supply or discharge pressurizing fluid in the elastic shrinking element (actuator) 23, a pressurizing fluid supply and discharge device is needed. Further, to stop and hold the second arm member 22 at specified position after moving to the first arm member 21, a pressurizing fluid supply and discharge device 26 is needed for applying a negative pressure in the gap between the inner side of the socket 20a and the ball 20b, and hence the entire structure is somewhat complicated.